Spark-plug and method of manufacturing spark-plugs.



IF. WI. FURBR. -sPARK PLUG Alm METHOD of'muuwcwmvm SPARK mms. APPLICATION FILED !AN.`20| ISIS' 191999541, Paentedapt. 26,1916.

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FREDERICK M. 'IfUtBEP-J, F FEVER/E, Mr

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Application filed January 20. lSS.

To all 1c/tom 'it may concern lle it known that l, Fnsnnnun lill'. FUarin, a citi-Zen of the nited States, residing at Revere, in the county of Suffolk and State of Massachusetts, have invented certain lmprovements in Spark-Plugs and Methods of ldanufacturing Spark-Plugs? of which the following description, in connection with vthe accompanying drawings, is a specilicatipn, like reference characters on the drawings indicating like part-s in the several figures.

i rlhis invention relates to spark plugs and to methods of manufacturing spark plugs.

T he exceedingly keen competition that has developed in the spark plug industry in recent years has placed a premium on economy in the manufacture of devices of this character, and in fact, has made thc practice of substantial manufacturing economies a necessity to the successful maintenance of a business in this field. Furthermore? the trade 1n recent years has become more exactmg in its requirements and is denianding a sturdier and more substantial plug, one far less fragile than has been acceptable in former years, and one that will successfully withstand hard usage. The attention of the trade seems particularly to have been directed to the matter of gas leakage through spark plugs; and the plugs novv placed upon the market are subjected to rigid tests designed to determine whether or not they are substantially gas tight and will remain so under operating conditions. Iihese conditions'have, of course, placed new I .requirements on the manufacturer, both as nto the construction of spark plugs and as to methods of ,manufacturing them; and it 1s the general object of the present invention to meet these requirements. l

Stated more specifically, the invention aims to devise a sturdy but simple and substantial construction of spark plug and an economical method of manufacturing such a plug.

The invention is particularly concerned with the mounting of the insulator in the shellor body of the spark plug. f

The invention will be readily understood from the following description of the preferred embodiment thereof, reference being made to the accompanying drawings, in vvhich- Figure l is a view in side elevation of a spark plug embodying the invention; Fig. 2 isa central, vertical, sectional View of t. e

Specification of Letters latent.

Patented Sept. 269 Serial No. 733e?.

plug shown in Fig. l; Fig. 3 is a view similaiI to Fig. 2 but showing the plug in the process of manufacture; and Fig. tisanother view similar to and 3 but showing the plug at a later stage in the process of manufacture.A

rlhe plug shown comprises a shell or body Q which may bc made out of har stock of hexagonal cross section, the lower part of this body being turned down to form a shank7 and the lower end of this shank being threaded to adapt it to be secured in an engine cylinder. The shell is drilled to form a"hore therethrough and is counterbored from its outer end, that is, the cud that projects out of the engine. cylinder7 to form anfinternal shoulder or scat 4v. lin insulator (i is positioned in the boroof the shell 2 and is provided with a circumferential cnlargement T. the ends of which form upper and lower shoulders S and 9, respectively. The shoulder l in the shell 2 forms a scat for the lower shoulder 9 of the insulator t3, and a gasket l is interposed between the surfaces l and 9. i sleeve l2 is shrunk in the outer end of the bore of the shell and bears at its inner end against the upper shoulder S of the insulator (l, clamping the insulator against the seat l in the shell. As indicated clearly in the drawings, the insulator is smaller in diameter. than are the parts of the shell or sleevethat encircle it so that a lateral clearance is provided between the peripheral surfaces of the insulator and the parts of the plug that inclose it and any danger of the insulator being crushed by the lateral grip or pressure of the shell on the. sleeve thus is avoided, the reduction in diameter of the insulator' being merely enough to accomplish this object. The insulator thus is held in the plug solely by the pressure exerted on the opposite ends of its enlarged port-ion 7.

According to the preferred method of manufacturing this spark plug, the shell 2 is supported on a die le (see Fig. 3) and is heated in some convenient manner, as for instan e.l by a flame from a Bumsen burner 16.' i

roble .0.1i the market and which are used to a considerable extent in spark plugs. The insulator 6 is then inserted in the bore of the shell with its -lower shoulder 9 resting on the gasket 10. The sleeve 12, which may be made of the same material as that from which theshell 2 is made, is then inserted in the outer' end of the bore of the shell and, before it has had time to heat up, is forced from the position in which it is shown in Fig. 3 to that in which it is shown in Fig. 4 by means of a plunger 18 or any other suitable device or mechanism. Preferably this plunger 18 is backed up by a spring or is operated by any one of numerous well known mechanisms designed to cause it to apply only a predetermined' pressure to the shell. The plunger forces tlle sleeve '12 into the shell with its inner end bearing against the upper shoulder 8 of the` insulator; and

through its pressure on this shoulder, forces` the shoulder 9 of the insulator against the gasket 10 with 'sufficient force to 'flatten the gasket out and cause it to conform to the seat fl on one side and to the shoulder 9 of the insulator on the other side. The sleeve should be made only a very few, say .one or two, thousan'dths of an inch less in external diameter than is the outer end of the 4bore `of the shell when it is hot. At about the same time-that the'plunger seats the insulator in'the shell in the manner just described,

and while the plunger still maintains its pressure on the sleeve 12, the source of heat is removed`and the shell 2 is allowed to cool. If desired7 the cooling operation may be hastened by the application of a current of:

air, water or oil; but even without hastening the cooling in this manner it requires only a few seconds for the temperatures of the shell and sleeve to equalize sufliciently. to

vcause the shell to seize theu sleeve 12 so firmly that manytimes the power would be required to move this sleeve relatively to the shell than was originally applied to the sleeve through the plunger 18 in seating the insulator in the shell. Of course the first grip of the shell on 'the sleeve is caused partly by the temperature of the sleeve rising, due to its absorption of heat from the shell. The plunger is then removed and the shell is taken out of the die A14. The insulator at this time is not only clamped in the shell with the pressure that was originally applied to it through the plunger 18, but as the shell continues to contract, this pressurev 4 of the shell and the part of the shell which' grips the sleeve 12 decreases as the shell continues to cool, and thus causes the parts 4 messer will not be disturbed thereafter by changes inthe temperature, since the sleeve then will be subjected to the same temperatures as is the shell and the two parts thus will expand and contract together. It is obvious that this method of manufacturing plugs avoids any necessity for machining the insulator and that it produces a plug in which a very tight joint is provided between the shell and the insulator since the gasket 10 is made to conform very closely to the shoulders 4t and 9 by the application to the insulator of suflicient pressure to produce this result. 1f desired a gasket 11 may be inserted between the edge of the sleeve 12 and the upper shoulder 8 of the insulator. The plunger 18 may be magnetized to aid in positioning the sleeve during the assembling operation.

use of a very sturdy insulator, since the up- Y per part of the wall of the shellcan be made and 12 toincrease their pressure on the enlargement 7 of the insulator. When the shell has once been shrunk on the sleevel in the mannerljuat described, its grip on the sleeve thinner than in most spark plug constructions; the sleeve 12 canbe made relatively thin, andthe diameter of the insulator above the shoulder 9 can be correspondingly increased. .Thebody 2 above the threaded portion of its shank can, of course, be made of any required diameter toaccommodate an insulator of the desired proportions. ln-

asmuch as a lateral clearance is provided between the peripheral surfaces of the insu lator and the parts .of the shell 2 and the sleeve'8 that encircle it, there is nb danger of the insulator being crushed by the contraction of the shell during the cooling opi eration. -This lateral clearance also allows the insulator to tip slightly in any direction that may be necessary, due to any unevenness in the shoulders 8 and 9, to permit it to seat itself properly on the gasket 10.-

Since the sleeve 12 fits loosely in or is very slightly smaller than the bore ofthe shell 2 when it is forced into the sleeve by the plunger18, the entire pressureof the plunger will be exerted on the shoulder 4 and a predetermined pressure thus can be applied` to each insulator. A The pressure necessary for this purpose can be determined with great accuracy and will, of course, be made such that there will be no danger of breaking a sound insulator, and yet will be suflicient to set the insulators down so firmly as toproduce a gas tight joint between the seat 4 and the shoulder 9.

The electrodes may be secured respec- Vtively 'in the shell and insulator in any convenient manner. The construction of the electrodes shown in the drawings and the method of securing them in the shell and insulator are too well known to require description.

It will be readily appreciated that a plug` of this construction requires extremely little skilled labor in its production, the shell and sleeve being produced by automatic nirequirements of the trade as above outlined.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. A spark plug, comprising a shell having-a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with upper and lower shoulders, respectively, at the oppo site ends of said enlargement, a seat in said shell for one of said shoulders, and a sleeve frictionally held in the bore of said shell and bearing on the other shoulder of said insulator, said sleeve, insulator and shell being of such dimensions as to provide a lateral clearance between the vperipheral surfaces of the insulator and the parts of said sleeve and shell that encircle it.

l 2. A spark plug, comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement With upper and'A lower shoulders, respectively, at the 0ppo site ends oit said enlargement, a seat 1n sald shell for one of said shoulders, and a sleeve frictionally held in the bore of said shell and bearing on the other shoulder of said insulator, said shell being shrunk on said sleeve and said sleeve operating to clamp the enlargement of the insulator against said seat solely by its pressure on one end of said enlargement and its ,frictional engagement with said shell.

In a spark plug, a shell, an insulator in said shell having a circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargen'ient, a seat in said shell for one of saidl shoulders, a sleeve bearing against the other shoulder, said shell being shrunk-on said sleeve, and a gasket between one of said shoulders and the part that bears against it, said sleeve, insulator and shell being of such dimensions as to provide a lateral clearance between the peripheral surfaces et' the insulator and the parts of said sleeve and shell that encircle it.

4. That improvement in the method of' much higher temperature than the sleeve ,with suiiicient pressure to clamp said enlargement of the insulator between said seat and said sleeve, and maintaining said pressure on the sleeve while the temperatures of the shell and sleeve become equalized sufliciently to cause the shell to grip the sleeve.

That improvement in the method of securing an insulator having a circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell` having an internal seat for one of said shoulders, which consists in placing a gasket between sa-id seat and the latter shoulder, forcing a loosely fitting sleeve into the shell against the opposite shoulder while the shell is at a much higher temperature than the sleeve with suiiicient pressure to clamp said enlargement between said seat and said sleeve, and shrinking sa'id shell on said sleeve while the parts are so clamped.

6. That improvement -in the method ofsecuring an insulator having a circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower shoulder, which consists in placing a gasket between said seat and said lower shoulder, forcing a sleeve of slightly smaller diameter than the bore ot' said shell into the outer .end of said shell against the upper shoulwith suiicient pressure to liatten said gasket between said seat and the lower shoulder, and maintaining said pressure'on said sleeve until the temperatures ot the shell and sleeve become equalized suiticiently to cause the shell to grip the sleeve.

7. That improvement in the method of securing an insulator having a circumferential enlargement with shoulders at the opposite ends ot' said enlargement, in a spark plug shell having an internal seat for one of said shoulders, which consists in interposing a gasketbetween said seat and one of said shoulders, forcing a loosely fitting sleeve into the shell against the other shoulder while the shell is at a much higher temperature than the sleeve, and at a temperature higher than that to which it will be subjected while in use, and maintaining suliicient pressure on the sleeve to distort the gasket while the shell and sleeve-equalize in temperature sufficiently to cause the shell to grip the sleeve.

In testimony whereof I have signed my name to this specification.

FREDERICK M. FURBER.

copies of this patent may be obtained for ve cents each, by addressing the Cominissioner of Patenti,

Washington, DJG. 

